Apparatus for applying stripes of solder to opposite sides of circuit boards

Abstract

Printed circuit boards 10 having connector terminals 14 and 16 overlaying contact pads 17 and 18 are loaded into fixtures 22 which are conveyor 31 advanced through a pair of solder applying stations 33 and 34 whereat solder is laid and melted at the junctures of the terminals and contact pads. As a fixture approaches a solder applying station, the conveyor is slowed down and a programmed controller 170 is enabled for operation. If a circuit board is sensed by a photodetector 172, a second photodetector is rendered effective to sense elements 176 projecting from a side of the fixture. The sensed elements 176 effectuate the generation of count pulses and output signals to control the movements of solder applying devices 36 to soldering sites where solder feed devices 136 lay discontinuous stripes of solder at the junctures of the contact pads and terminals.

What is claimed is: 
     
       1. An apparatus for applying stripes of solder to two rows of terminals overlaying contact pads arrayed along opposite sides of a printed circuit board, which comprises: an open frame holder for receiving and supporting opposed edges of a printed circuit board;   a pair of solder applying devices each having a solder feeding tube for guiding a strip of solder through an exit end thereof;   a closed loop conveyor means for continually advancing said holder through a pair of soldering sites each spaced from a respective exit end of said solder feeding tubes;   means for advancing and withdrawing said solder applying devices to move the exit end of a corresponding solder feeding tube into and out of a soldering site;   means for controlling the speed of said closed loop conveyor means and the advance and the withdrawal of said solder applying devices;   first means positioned at each solder applying device for sensing the presence of a frame holder approaching a soldering site for generating a signal to enable operation of said controlling means;   means advanced with said frame holder having a series of uniformly spaced elements;   second means positioned at each solder applying device for sensing said uniformly spaced elements as said elements move past a corresponding soldering site and for generating and applying pulses to said controlling means;   means responsive to the receipt of a predetermined number of pulses by said controlling means for advancing a solder applying device to a corresponding soldering site;   means responsive to the receipt of a subsequent pulse for feeding a solder strip through the tube of the advanced solder applying device to said soldering site;   means for melting the solder fed to said soldering site; and   means for rotating said holder during its advance between soldering sites to present a different side of the printed circuit board to each one of the solder applying devices.   
     
     
       2. An apparatus as defined in claim 1 wherein said first sensing means resets said enabled controlling means upon failure of said sensing means to sense the presence of a printed circuit board in said frame holder. 
     
     
       3. An apparatus as defined in claim 1 for applying discontinuous stripes of solder to discontinuous rows of terminals, wherein said controlling means disrupts the solder feed upon receipt of a predetermined number of pulses indicative of the discontinuance of the terminals, and commences said solder feed upon receipt of subsequent number pulses indicative of the first of the remainder of said terminals. 
     
     
       4. An apparatus for applying stripes of solder to opposite sides of printed circuit boards, which comprises: conveyor means including at least four sprockets mounted on vertically extending shafts and a closed loop belt mounted on said sprockets;   a plurality of spaced mounting plates secured to said belt;   a U-shaped holding fixture rotatably mounted on each of said mounting plates to extend in a horizontal plane for receiving a printed circuit board between the arms of said U-shaped fixture;   a pair of soldering devices spaced along the path of movement of said holding fixture, each of said soldering devices including a pair of feed wheels for advancing a strip of solder into a tube having an exit end adjacent to the path of movement of said holding fixtures and spaced from a soldering site in proximity to the path of movement of a printed circuit board received in said holding fixture;   means for rotating at least one of said sprockets to drive said conveyor means at a first predetermined speed to successively move said holding fixtures to the soldering sites associated with said soldering devices;   means responsive to the approach of each holding fixture to a soldering site for controlling said sprocket rotating means to drive said conveyor means at a second slower predetermined speed and for reinitiating the conveyor means to drive the fixtures at said first predetermined speed as the fixture leaves the soldering site;   means operated following the slow down of said conveyor means for moving the soldering devices toward the path of movement of the fixtures to position the exit ends of the tubes in the soldering sites, and for initiating operation of said feed wheels to advance the solder strip into the tubes;   means for heating the soldering sites to melt the solder fed onto the moving printed circuit boards; and   means for rotating said fixtures moving from a first soldering site to the second soldering site to present the opposite side of each printed circuit board to the second soldering device.   
     
     
       5. An apparatus as defined in claim 4 wherein said conveyor speed control means and said soldering device moving means comprise: a first photodetector means for sensing the approach of a holding fixture to a soldering site and generating an enable signal;   a coded bar attached to each mounting plate having a predetermined number of fingers spaced to control the generation of count pulses;   a second photodetector means for sensing the fingers on the coded bar for generating count pulses; and   a controller initiated into operation by said enable signal and responsive to said count pulses for operating said soldering device moving means.   
     
     
       6. An apparatus as defined in claim 5 wherein said controller responds to a first predetermined number of count pulses to raise the soldering device and interrupt operation of said solder feed wheels and responds to a second predetermined number of count pulses to again lower the soldering device and reinitiate operation of the solder feed wheels for laying an interrupted stripe of solder on a printed circuit board passing through a soldering site. 
     
     
       7. An apparatus as defined in claim 4 which includes: sections of horizontal trackways extending between said sprockets in a plane elevated from the plane of said sprockets;   rollers mounted on horizontal shafts extending from said holding fixture for movement along said trackway sections to support said belt and said holding fixture; and   flat plates mounted above said sprockets in the plane of said trackways and extending between ends of adjacent trackway sections to support said belt and said fixture as said fixture moves about said sprockets.   
     
     
       8. A method of applying solder stripes to junctions of connector terminals and contact pads arrayed along opposite sides of a printed circuit board, which comprises: rotatably mounting a plurality of holding fixtures on a closed loop conveyor belt;   mounting an assembly including a connector and a printed circuit board in each of the holding fixtures so that the board extends horizontally away from the conveyor belt;   continually advancing a succession of assembled connectors and printed circuit boards through a pair of spaced soldering sites, said connectors having their terminals abutting contact pads on opposite sides of the circuit boards;   sensing the approach of a printed circuit board to a soldering site and generating an enabling pulse to condition a controller for operation;   generating count pulses indicative of the advance of the circuit boards through the soldering sites;   applying said count pulses to said conditioned controller to produce a succession of control signals;   advancing a solder dispensing tube in response to a first control signal into position to direct a solder strip at the junctions of the abutted contacts and terminals on the board moving through a soldering site;   feeding the solder strip through the tube to emanate toward the moving abutted contacts and terminals in response to a second control signal;   applying a first stream of hot air to the abutted contacts, terminals and the adjacent sections of the printed circuit boards approaching the soldering sites to heat the abutted contacts and terminals to a temperature sufficient to melt the solder emanating from the tube and directed against the abutted contacts and terminals; and   rotating the holding fixtures to turn the boards over after leaving a first soldering site and during advance to the second soldering site.   
     
     
       9. A method as defined in claim 8, which further includes: applying a second stream of hot air to the soldered terminals and contacts leaving the soldering sites.   
     
     
       10. A method as defined in claim 8 which includes: sensing the presence of a board in a holding fixture as the fixture approaches a soldering site; and   interrupting operation of said controller upon failure to sense the presence of a circuit board in a fixture.